Why Do Male Dogs Have Nipples?

If you are wondering why male dogs have nipples, you may be curious to know why on earth they are there. As far as you have known, male dogs don't have puppies, and most importantly, they won't ever be nursing, so what gives? A common answer to this question is that male dogs have nipples "just because." After all, even among humans, men are also blessed with a pair of nipples! But you may already know that "Why do Dogs" isn't happy with such a generic answer, so we decided to further investigate.

A Lesson in Anatomy

All dogs have nipples, and that includes neutered males, spayed females, intact males, and of course, intact females. Nipples in dogs are displayed side-by-side starting from the chest area all the way to the inguinal area, near the back legs. The amount of nipples a dog has depends on its size. In smaller dog breeds, eight nipples is the average; whereas, in larger breeds the average is ten. Nipples have different names depending on their anatomical location. Generally, dogs who have ten nipples have the following:

One pair of cranial thoracic nipples

One pair of caudal thoracic nipples

One pair of cranial abdominal nipples

Once pain of caudal abdominal nipples

One pair of inguinal nipples

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An Important Purpose

The primary purpose of nipples is to provide puppies with milk. When mother dog whelps, she will be supplying milk produced by the mammary glands and secreted from several ducts arranged around the tip of the nipple. Since male dogs do not have babies, and as such, do not have to nurse puppies, their nipples remain in what is known as a "rudimentary state."

A Matter of Economy

Mammary glands are simply modified sweat glands, explains veterinarian Dr. Justin Lee in the book: " It's a Dog's Life...but It's Your Carpet." Nipples are present in both male and female embryos during fetal development. Actually, it can be said that early in development, male and female human embryos are essentially the same with no distinguishing features, almost as if made from a virtual "cookie cutter."

Then, later on, as sex hormones kick in, the features of male body parts are crafted making male and female embryos easier to differentiate. This is known as "sexual differentiation." However, even once born, in female and male puppies the nipples remain indistinguishable at birth. It is only later on in life, when female sex hormone kick into high gear, that a female dog's nipples will cause them the enlarge and eventually secrete milk. This becomes noticeable when female dogs are pregnant and ready to whelp or when they develop a false pregnancy.

So Why Do Male Dogs Have Nipples?

Why male dog nipples have stuck around for so long in both male dogs and people remains still a mystery considering the minimal purpose they serve. While at least in human men, nipples can make a handy new location for body piercings, dogs sure have nothing trendy going on there. While an exact answer as to why males have nipples has yet to be found, in the meanwhile, evolutionary biologists assume that adaptive pressure simply wasn't strong enough to wean them out.